In many areas of the art there is a need for conductive pigments with which, for example, electrically conductive plastics, paints, coatings, fibers or the like, which provide shielding from antistatic or electromagnetic waves, can be prepared. Conductive carbon black is employed in large amounts for this purpose, but because of its high light absorption it cannot be employed for pale or colored coatings.
Another disadvantage is the high absorption of carbon black in the IR range, which leads to an in many cases unwanted heating of the coated articles in sunlight, for example.
EP 0 373 575 discloses conductive platelet-shaped pigments which have as conductive layer an antimony-doped tin oxide, a thin layer of silicon dioxide being arranged between the conductive layer and the substrate. The application of an additional layer to the substrate means a considerably increased outlay for the preparation and makes the pigment more expensive.
DE 42 13 747 A1 describes conductive pigments which have, as conductive layer on a substrate, a halogen-doped tin oxide and/or titanium dioxide layer.
Substrates having a phosphorus-doped tin oxide layer are known from DE-A 44 35 301.
However, the conductive pigments of the prior art are not sufficiently opaque and therefore not suitable for preparing decorative coatings. Furthermore, the pigments have conductivity values which do not meet all the high requirements.
There was therefore a need for stable, electrically conductive pigments which are opaque and which impart not only conductivity but also a decorative appearance to coatings or plastics.
EP 0 587 102 discloses the coating of barium sulfate with a niobium- or tantalum-doped tin dioxide layer.
In JP H6-345 430, tin dioxide particles are doped with from 0.1 to 10% by weight of pentavalent niobium or tantalum.
WO 96/06437 discloses electrically conductive powders comprising doped tin dioxide powder.
The coating of platelet- or needle-shaped substrates with an electrically conductive doped tin oxide or titanium dioxide layer, however, is not described in the prior art.